Isolated rat liver mitochondria, freed from microsomes and lysosomes contaminants, were maintained at 0-4 degrees C for several days using an appropriate medium and energy source. It was observed that the phospholipase A2 activity of mitochondria deficient in vitamin E is higher than in normal mitochondria, and that the presence of vitamin E in the preservation medium diminishes the phospholipase A2 activity in deficient mitochondria. In vitamin E deficient mitochondria up to 45% of phospholipids was digested by the endogenous phospholipase with little loss in the energy linked function or without considerable activation of the latent enzymes monoamine oxidase and ATPase. These results are consistent with the occurrence of phospholipids in the mitochondrial membrane which would render it more accessible to the action of phospholipase A2.